Tight junctions, which are also called “zona occludens”, form a regulated, semipermeable barrier in the intercellular spaces within sheets of epithelial or endothelial cells. The properly regulated formation of tight junctions is an important aspect of the normal development of tissues such as the skin, and maintenance of these junctions may assist in suppressing the formation and spread of tumors. Inadequate or improperly regulated epithelial or endothelial barrier function contributes to the initiation, maintenance, and exacerbation of inflammation in tissues such as the gut, lungs, and the like. Tight junctions also form a “fence” separating the apical and basolateral regions of these cells' membranes, allowing the establishment of different physiological environments on the opposite sides of a cell sheet, such as the different physiological environments required for transport of materials across the intestinal epithelium. It has also been proposed that tight junctions contain aqueous pores, with paracellular transport between the cells of an epithelial or endothelial sheet occurring through these pores. In order to develop more effective treatments for conditions involving disruption of epithelial or endothelial barrier function or unregulated transport across the epithelium or endothelium, such as inflammatory bowel disease or skin disorders such as psoriasis or contact dermatitis, the identification of proteins that play a role in tight junctions is critical in understanding and treating such diseases and disorders.